1. Field of the Invention
The present invention relates in general to an improved high energy density welding method, and in particular, to a new and improved high energy density welding method for keyhole welding with an improved joint design.
2. Description of the Related Art
High energy density welding is a term of art employed for three specific types of welding processes, laser welding, plasma arc welding, and electron beam welding. In these welding processes, the two members that are to be welded are tightly abutted against each other and then welded together.
It is known in the art for keyhole welding or keyhole mode welding, which is a high energy density welding process, to position a gap between the members to enhance penetration ability. Merely separating the members to be joined by a fraction of an inch facilitates the welding process. The recognized problem with this separation technique is how to control the gap as the already deposited weld metal shrinks. This closes the gap. The difficulty of maintaining the gap by using spacers, wires, shims, etc. outweighs the benefits. Tack welds can be used, but these cause local penetration problems. If the joint is tack welded intermittently to keep the gap open, the tack weld itself can break or cause penetration problems due to deposited tack weld material making the joint thicker.
Moreover, thick sectioned (greater than 1/4" thick) welding requires material removal from the joint area before welding. This enables arc energy to impinge on a thinner section near the bottom of the joint to ensure penetration through the joint. This joint preparation usually requires a groove to be formed which is typically a "V" or a "U" configuration.
One reference, Proceedings of the Electron Beam Welding Symposium, edited by Edward R. Funk, on page 257 illustrates a step-type joint design as shown in FIG. 1. While this reference shows a gap, it describes that the purpose of the joint design is for self-aligning, self-supporting and self-fixturing. It then lists the disadvantages with this type of joint design such as difficulty to fabricate, difficulty to weld, difficulty in controlling quality, requiring a backup shield, difficulty in inspection, the provision of a gap always in the joint, and difficulty to assemble. This reference also illustrates a lip type joint on page 255 and shown in FIG. 2. The disadvantages with this weld joint include the difficulty to fabricate, the relative difficulty to weld, and the need for added material for the lip.
U.S. Pat. No. 4,639,574 discloses a method and apparatus for automatically welding together edges of sheet metal to form a sealed joint in the fabrication of duct work.
U.S. Pat. No. 4,709,604 describes a tool joint reworking device for milling exterior surfaces and refacing both shoulders of a two-shoulder tool joint.
U.S. Pat. No. 4,645,897 is directed to a method and apparatus for aligning two workpieces for butt-welding and with removal of weld upset.
Accordingly, there is a need for a high energy density welding method which provides a controlled gap so as to enhance the welding process. This welding method must provide for welding thicker sections of material with less heat input and eliminate the necessity for filling in grooves in prepared joints with multiple layers of weld material.